Field of the Invention
The present invention relates to modular lighting. In particular, it relates to magnetically restrained lighting systems and methods of use.
Description of Related Art
Modular track lighting systems have been available for decades and were originally designed to use incandescent light bulbs. These systems typically have included fixtures that are mounted to rigid tracks with spring contact tabs that are rotated into contact with linear conductors, thereby providing electrical power to the lighting module. For electrical mains voltage safety, these linear conductors are shielded from direct finger contact. More recently, suspended rail and wire systems have been introduced that include insulation piercing contacts and/or use inherently safe lower voltages. These systems generally require tools for mounting individual lighting fixtures.
In recent years, there has been interest in solid-state lighting systems, in particular, light emitting diodes (“LEDs”). These systems tend to be smaller in size, longer-lived, and more efficient than standard incandescent light bulbs. Magnetic attachment of LED lighting modules has been proposed, for example, in U.S. Pat. Nos. 7,726,974 and 7,806,569 to eliminate the need for a tool to attach the LED lighting modules along the length of the track.
Although visible LEDs are efficient in that they do not generate wasteful infrared radiation and they generate less heat than incandescent systems, they do create some waste heat that must be removed from the emitting junction by thermal conduction to avoid degradation in performance or reliability since they are more sensitive to heat than incandescent systems. Existing magnetic attachment systems have limited thermal cooling efficiencies which restrict their power capability for general illumination applications with high-brightness LED assemblies since the greater the number of LEDs, the greater the heat generation and the greater the degradation problem. The proposed systems in U.S. Pat. Nos. 7,726,974 and 7,806,569 rely upon cooling by thermal conduction directly through the magnetic material and convection cooling through passive air movement near the LED subassembly. Neodymium and ferrite magnets have thermal conductivities that are approximately 10, 20, and 40 times less than that of iron, aluminum, and copper, respectively. The thermal conductivity of air is three orders of magnitude less than iron. Excess thermal interfaces in the conduction path between the LED subassembly and the external heat sink generally add to cooling inefficiencies.
Existing magnetically attached systems often include interface elements that require precision mechanical tolerances for proper attachment. Planar magnets and rigid contacts “rock” on non-planar surfaces reducing contact areas for thermal conduction or the ability to accommodate mechanical variation. Also, the number of electrical contacts that can be attached uniformly is limited. Thermal expansion effects further increase the level of precision required in these interfacing parts. Note also that lighting modules that are exposed to heat often change tolerances due to frequent heating and cooling cycles.
In addition to track lighting systems, the higher performance of solid state lighting has generated interest in replacement systems suitable for existing incandescent screw sockets. Available one-piece standard screw-in incandescent bulb replacements using solid state lighting combine less reliable electrolytic capacitors with higher reliability and more expensive LED subassemblies in a single field replaceable unit. Differences in functionality such as dimming in the integrated electronics result in stocking completely different units or including unused functionality and unnecessary parts cost. Although two piece designs have been proposed, these proposals have not provided details on how a mechanical, electrical, and thermally efficient mounting of the LED subassembly can be accomplished to the socket with higher modularity.
Even in current solid state lighting systems that are not meant to fit in an existing incandescent lighting fixture, differences in functional attributes including power output, emitted light spectral, or directional characteristics create increased costs to businesses and consumers. A need exists for a highly-modular, robust system for creating reliable interconnecting between lighting system elements.
Rapidly rising prices for rare earth elements has increased the cost of relatively strong magnets and as such, while useful, they are becoming impractical for lower cost lighting systems. Existing lighting systems fail to simultaneously optimize the mechanical, electrical, and thermal performance especially with smaller, less expensive magnets which require the stronger magnets to properly make and retain a connection.
Insulation piercing contacts have been proposed for electrical safety and environmental considerations, but the mechanical forces required to pierce insulators may be higher than the magnetic force available even with use of rare earth magnets. Insulation piercing contacts permanently change the system which may introduce aesthetic or safety issues when a module is removed or moved within the system. There is a need for alternate approaches for electrical safety that provide greater flexibility in attachment without damage or requiring a onetime attachment.
Lighting modules can be difficult to seal from the environment while maintaining electrical/mechanical and thermal performance and this adds to the difficulties with magnetic attachment of an electrical connection for a lighting system.
While some systems attempt to address one or more of these problems, a need still exists for a solid state lighting system solution that provides a robust mechanical, electrical and/or thermal interface attachment mechanism using magnetic materials that is modular and includes a wide range of fixture mounting options.